Technical Field
The present invention generally relates to semiconductor device fabrication, and more particularly, to devices and methods for pattern density control to form assist features in directed self-assembly applications.
Description of the Related Art
Directed self-assembly (DSA) of block copolymers (BCPs) has emerged as a useful tool in semiconductor processing. A BCP is composed of two or more strands of chemically distinct polymers binding linearly together. BCPs, upon annealing, can phase-separate into uniform polymer micro-domains whose dimension is about tenths of nanometer. DSA includes providing physical guides, mandrels or templates with chemical contrast, to direct BCPs micro-domains into useful structures, e.g., parallel lines and the like. DSA may be employed, e.g., to form interconnect lines, spacers and/or contacts.
Graphoepitaxy Directed Self-Assembly (DSA) of block copolymers (BCPs) for via/contact shrink processes utilizes a topographical guiding pattern to drive feature assembly. Spin-coating BCPs over topographical substrates results in film thickness variation across a wafer, especially when pattern density varies. Such thickness variations affect pattern transfer and restrict allowable designs. Adding assist features (or “fill”) to balance local pattern density can be adopted to reduce variations; however, state-of-the-art DSA assist features only consider single plane density control.